Warm, damp, dark environments provide favorable conditions for growth of infectious biological microorganisms, allowing bacteria, viruses, fungi, and their associated odors to proliferate. For example, foot perspiration within shoes promotes warmth and dampness, while closed shoes stored in dark closets may fail to admit enough broad spectrum ambient light to control pathogen levels. Excessive levels of harmful microorganisms sustained in enclosed shoes may cause or promote various foot maladies.
It is well-known that exposure to ultraviolet (UV) light of certain wavelengths, intensities, and durations can destroy or inhibit growth of surface pathogens. For instance, germicidal lamps that emit UVC radiation are used to treat waste water for the purpose of reducing organic content. U.S. Pat. Nos. 4,981,651 and 5,978,996 describe the use of UV light for sterilization; however, not all UV light wavelengths are germicidal. The UV spectrum spans wavelengths from 10 nm to 400 nm. The band from 320 nm to 400 nm is designated as UVA; 280 nm to 320 nm is UVB; and 100 nm to 280 nm is UVC. Germicidal UV light, the type that destroys microorganisms, is limited to a wavelength range from 240 nm to 280 nm, in which maximum germicidal efficiency coincides with a wavelength of 254 nm. UVA and visible light, which includes a near-UV component, have been shown to inhibit growth but not to destroy pathogens.
One concern with harnessing UV light, which is a form of short wavelength, high energy radiation, is that UV light can cause damage to human tissue. Eyes are especially vulnerable when exposed to direct incidence of UV light. Thus, any application of high energy radiation, including UV light, should protect against unwanted exposure.
Many air filtrations systems have filters to clean the air. A typical air filter is the HEPA filter that is designed to remove pollens, dust, smoke and other tiny particles that may attribute to odor. Additionally, some air filtration systems use carbon to help remove pollutants from the air. Other air filters, such as those described in U.S. Pat. Nos. 7,951,327 and 7,927,554, use titanium dioxide (TiO2), in conjunction with a UV light source, in a process called photo-catalytic oxidation to destroy bacteria, volatile organic compounds, and other airborne pollutants to sanitize the air.